Field of the Invention
The present invention relates to a rotor structure including a rotor core provided with a central hole and a hole for magnet (a magnet hole) formed in an outer circumferential portion, a permanent magnet mounted in the magnet hole, and a rotor shaft press-fitted in the central hole.
Related Art
Motors for hybrid vehicles and others are severely demanded for size reduction more than regular motors. Downsized motors tend to rise in temperature. Such a motor is more likely to cause a decrease in magnetic flux of a magnet at high temperature than in conventional motors. To prevent this decrease in magnetic flux density at high temperature, magnet material would be mixed with rare metal such as dysprosium. The rare metal is however expensive and hence leads to cost increase.
In order to reduce the amount of magnet material and also decrease the amount of electric current to a stator to thereby reduce the amount of heat generation of a motor, it is an effective method to prevent leakage of magnetic flux in the rotor core and reduce consumption current of the motor. In Patent Document 1, accordingly, a rotor core is split into outer circumferential pieces in which magnetic flux will flow and an inner circumferential piece, which are coupled by non-magnetic bridges, to prevent the magnetic flux from leaking to the inner circumferential piece. Patent Document 2 also discloses that a bridge for reinforcing the strength of a magnet insertion hole is made of non-magnetic material to prevent magnetic flux leakage.